Impurities immersed in the surrounding ultracold Bose gas experience interactions mediated by the surrounding many-body environment. If we focus on two impurities that are close enough to each other, we can form a bipolaron pair. Here, we discuss how standard methods based on linearization of the condensation field yield valid results only for sufficiently large impurity separations in weak coupling regimes. We show how these shortcomings can be improved within the Born-Oppenheimer approximation by accounting for the inter-Boson interaction already at the mean-field level.

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